Thermal radiation system for soil stabilizer

ABSTRACT

A thermal stabilizer assembly consisting of a vertical tubular convection cell mounted in a body which is to be thermally stabilized, the convection cell being provided with a heattransmitting fin configuration at its upper portion for heat transmission to the atmosphere. The fin configuration may consist of auxiliary metal tubes clamped to the cell by metal straps. The auxiliary tubes may be arranged in layers. The auxiliary tubes may consist of relatively small auxiliary tubes clamped in relatively large auxiliary tubes, both in heat-conducting contact with the main convection cell. The fin configuration may alternatively consist of flanged vertical bars clamped around the vertical convection cell by metal straps.

United States Patent [1 1 Beach 1 Sept. 4, 1973 1 1 THERMAL RADIATION SYSTEM FOR SOIL STABILIZER [76] Inventor: Winfield G. Beach, 808 Lakeview Trailer Ct., Fairbanks, Alaska 99701 [22] Filed: Apr. 11, 1972 [21] Appl. No.: 242,979

Related US. Application Data [63] Continuation-impart of Ser. No. 35,629, May 8, 1970,

Pat. No. 3,656,547.

[56] References Cited UNITED STATES PATENTS 1,920,800 8/1933 McCausland ..165/183X 3,472,314 10/1969 Balch 165/106 FOREIGN PATENTS OR APPLICATIONS 707,514 4/1931 France 165/183 894,691 4/1962 Great Britain 165/154 Primary ExaminerAlbert W. Davis, Jr. Att0rney1-1yman Berman et a1.

[5 7 ABSTRACT A thermal stabilizer assembly consisting of a vertical tubular convection cell mounted in a body which is to be thermally stabilized, the convection cell being provided with a heat-transmitting fin configuration at its upper portion for heat transmission to the atmosphere. The fin configuration may consist of auxiliary metal tubes clamped to the cell by metal straps. The auxiliary tubes may be arranged in layers. The auxiliary tubes may consist of relatively small auxiliary tubes clamped in relatively large auxiliary tubes, both in heatconducting contact with the main convection cell. The fin configuration may alternatively consist of flanged vertical bars clamped around the vertical convection cell by metal straps.

10 Claims, 18 Drawing Figures PATENTED SEP 4 I975 SHEET 1 BF 4 mm? 4 m5 3.756. SHEET t (If 4 313 I THERMAL RADIATION SYSTEM FOR SOIL STABILIZER This is a continuation-in-part of the application of Winfield G. Beach, Ser. No. 35,629, filed May 8, 1970,

now US. Pat. No. 3,656,547, granted Apr. 18, 1972, entitled Thermal Radiation System for Soil Stabilizer."

This invention relates to heat transfer systems, and more particularly to thermal stabilizer assemblies for stabilizing soil masses or bodies of water subjected to freezing and thawing effects.

A main object of the invention is to provide a novel and improved thermal stabilizer assembly adapted for use in areas subject to soil heaving and other undesirable actions induced by changing temperatures, the assembly being relatively simple in construction, being efficient in operation, and involving inexpensive parts.

A further object of the invention is to provide an improved thermal stabilizer assembly which may be employed for stabilizing bodies of water or masses of soil by the action of liquid in a convection cell inserted in the material to be thermally stabilized, the improved assembly providing more efficient and more rapid heat transmission to or from the atmosphere with respect to the convection cell, involving very simple components, being relatively compact in size, being arranged so that it will operate continuously without attention or maintenance once filled with appropriate liquid, and providing improved heat radiating or absorbing capacity for the associated thermal stabilizing system.

A still further object of the invention is to provide an improved fin configuration for a thermal stabilizer convection cell, the configuration having high heat transmission capacity, having maximum heat conductivity with respect to the convection cell, and providing effective stabilizer effects continuously over long periods of time without requiring attention, adjustment or other types of maintenance operations.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

FIG. 1 is a perspective view of a thermal stabilizer convection cell provided with one form of improved fin configuration in accordance with the present invention;

F IG. 2is a horizontal cross-sectional view, to a somewhat enlarged scale, taken substantially on the line 2--2 of FIG. 1;

FIG. 3 is an enlarged fragmentary top plan view of a modified form of improved convection cell and fin assembly according to the present invention;

FIG. 4 is a top plan view of another modification of an improved convection cell and fin assembly constructed in accordance with the present invention;

FIG. 5 is an elevational view of the thermal stabilizer assembly of FIG. 4;

FIG. 6 is a fragmentary top plan view of a further modification of convection cell and fin assembly according to the present invention;

FIG. 7 is a fragmentary top plan view, similar to FIG. 6, but showing an additional modification of the fin as sembly;

FIG. 8 is a fragmentary top plan view, similar to FIG. 6, but showing another modification of the improved fin assembly of the present invention;

FIG. 9 is a fragmentary top plan view, similar to FIG. 6, but showing still another modification of the improved stabilizer assembly of the present invention;

FIG. 10 is a fragmentary top plan view, similar to FIG. 6, but showing still another form of fin configuration according to the present invention;

FIG. 11 is a top view of another modification of an improved thermal stabilizer assembly according to the present invention, employing flanged vertical bars as fins;

FIG. 12 is an elevational view of the thermal stabilizer assembly of FIG. 11;

FIG. 13 is an enlarged end elevational view of one of the flanged fins employed in the assembly of FIGS. 11 and 12;

FIG. 14 is an enlarged perspective view of a heattransmitting fin employed in the thermal stabilizer assembly of FIGS. 11 and 12;

FIG. 15 is a perspective view of a modified form of fin element which may be employed in the thermal stabilizer assembly of FIG. 11;

FIG. 16 is an enlarged end view of the fin element of FIG. 15;

FIG. 17 is a perspective view of another modified form of fin element which may be employed in the thermal stabilizer assembly of FIG. 11; and

FIG. 18 is an enlarged end view of the fin element of FIG. 17.

Referring to the drawings, and more particularly to FIGS. 1 and 2, 15 generally designates an improved heat transfer assembly constructed in accordance with the present invention. The assembly 15 is intended to stabilize a region of material, such as soil, or the like, to prevent undesirable ground heaving and similar effects caused by differences in temperature between the surface portions of the mass, for example, the portions at the top, exposed to the atmosphere, and the lower portions of the mass, remote from the ground surface. In regions having a cold climate, the ground temperatures are naturally much lower at the surface than beneath the surface during the fall, winter and spring months. This substantial difference in temperature produces undesirable effects, such as ground heaving, and it is therefore highly important to minimize the differences in temperature, for example, adjacent structures, such as piles or the like associated with structural assemblies. The device 15 is designed to remove heat from the soil mass, or from any other material in which it is employed.

.The stabilizing device 15 comprises a metal inner casing 16 with a closed bottom end and being adapted to contain a suitable liquid which can circulate by convection therein responsive to the presence of a substantial temperature differential between its upper and lower portions.

Secured on the upper portion of the casing 16 is a heat transfer assembly, designated generally at 17, for transferring heat from the top portion of casing 16 to the atmosphere at a relatively rapid rate. The heat transfer assembly 17 comprises a plurality of metal tubular fins 18 positioned around the upper portion of the casing 16 and clamped thereagainst by a plurality of spaced peripheral metal clamping bands 19 which bind the tubular fins 18 into close heat-conductive contact with the casing 16. As shown in FIG. 2, the tubular fins 18 are relatively small in diameter as compared with the inner casing 16 and completely surround the inner casing, being held in firm heat-conductive contact with each other as well as with the inner casing by the clamping action of the bands 19.

The temperature stabilizing apparatus is mounted in the soil adjacent to the structure where soil stabilization is required, the lower portion of the casing 16 being buried in the ground, for example, in the manner illustrated in FIG. 1, where ground level is designated at 20. Thus, the lower portion of casing 16 extends downwardly into the ground to a substantial depth, whereas the heat transfer assembly 17 carried by the upper portion of the device is supported somewhat above ground level. Thus, the assembly 17 is sufficiently elevated to allow free circulation by convection of air through the tubular fins 18.

In operation, assuming that a substantial temperature differential exists between the atmosphere and the region in the ground adjacent to the lower portion of casing 16, the temperature differential will generate convection of liquid in the casing 16, causing the liquid in the casing 16 to develop convection action causing the liquid to move past the wall of the casing and transfer heat thereto.

In a typical situation, liquid flows upwardly through the central portion of the casing toward the top surface of the liquid and then flows outwardly and downwardly past the inside surface of the casing wall. Heat is transferred through the casing wall. Heat is transferred through the casing wall to the tubular fins l8. Atmospheric air moves upwardly through the fins 18 because of the temperature differential thus created, and the upwardly moving air passing through the fins carries off a substantial amount of heat from the fins, the heated atmospheric air emerging from the top ends of the fins, as shown by the arrows in FIG. 1. Thus, an atmospheric convection action is generated around the fins 18 which transfers the heat to the atmosphere. The net result is to reduce the temperature differential between the atmosphere and the region in the soil adjacent to the lower end of casing 16, thereby providing the desired soil stabilization effect. I

FIG. 3 diagrammatically illustrates a modification of the system shown in FIG. 2 wherein a plurality of layers of heat-transfer fins are employed instead of a single layer. Thus, in FIG. 3 a continuous inner layer of tubular cooling fins 18 is provided extending completely around the inner casing 16, and superimposed on the inner layer of fins are additional tubular fins 22 which are clamped against adjacent fins 18,18 by the outer metal clamping bands, shown at 23. It will be seen that as in the case of the embodiment of FIGS. 1 and 2, the inner tubular fins 18 are further conductively bridged by respective outer tubular fins 22, which serve as heat conductors, as well as auxiliary convectors acting in the same manner as the inner fins 18. The heat-radiating surface is thereby considerably increased, as well as the convection action, providing a substantial increase in the ability of the resultant assembly to transfer heat away from the upper portion of the liquid convection casing 16.

FIGS. 4 and 5 illustrate a further embodiment of the invention employing the above described general principles. The embodiment illustrated in FIGS. 4 and 5 is especially suitable for conditions such as those wherein the snow level is unpredictable and may possibly be of substantial height. The assembly shown in FIGS. 4 and 5 comprises an inner liquid convection casing 16, as above described, wit a heat transfer assembly, shown generally at 30, clamped thereto at its upper portion. The assembly 30 comprises a plurality of relatively small-diameter metal tubular fins 31 which are clampingly secured in respective larger-diameter outer fins in the amnner illustrated in FIGS. 4 and 5 by metal tension bands. Thus, each tubular fin 31 is received in a larger metal tubular fin 32 with the top ends of the metal tubular inner fins 31 protruding upwardly from the top ends of the larger tubular fins 32 and clampingly engaged by a circumposed metal clamping band 33. The larger fins 32 are formed with circumferential slots 34 at their lower portions and another clamping band is tightly engaged around the lower portions of the inner metal tubes 31, the slots 34 providing clearance for the lower clamping band 35. As shown in FIG. 5, the lower ends of the inner tubes 31 terminate substantial distances above the lower ends of the metal tubes 32, and the lower poritions of the larger metal tubes 32 are clamped against the casing 16 by the provision of a circumferential metal clamping band 36. The slots 34 are preferably located above the highest expected snow level.

As shown in FIG. 5, the top ends of the outer tubular fins 32 slope downwardly and outwardly and the bot tom ends of said tubular fins slope upwardly and outwardly. The top ends of the inner tubular fins 31 slope upwardly and outwardly and the bottom ends of said inner fins slope upwardly and outwardly. The lower ends of the inner fins 31 are located a substantial distance above the expected maximum snow level.

In operation of the assembly of FIGS. 4 and 5, heat is conducted away from the top portion of the convection casing 16 to the large fins 32 and also to the small fins 31. Under conditions where the snow level is relatively low, falling below the open bottom ends of the large tubular fins 32, cooling convection currents of air from the atmosphere fiow through the fins in the same manner as above described in connection with the preceding embodiments of the invention. This would provide the desired stabilization action, since the heat conducted to the small and large tubes is carried off by the atmospheric air circulating upwardly through the tubes. If the snow level should rise above the lower ends of the large tubes 32, sealing said lower ends, atmospheric air enters the top ends of the large tubes 32 and circulates downwardly therein and then upwardly through the smaller inner tubes 31, providing the desired cooling action. Also, atmospheric air can flow into the larger tubes 32 through the slots 34 and then flow through the lower ends of inner tubes 31 upwardly through the inner tubes, adding to the transfer of heat from the upper portion of casing 16 to the atmosphere. The resultant effect is to insure proper temperature stabilization of the soil, or other material with which the apparatus is used, under a wide range of snow level conditions.

As above mentioned, outer clamping bands 36 are employed at the lower portion of the assembly, as well as the upper portion thereof around the upper portions of outer tubes 32 to clamp said outer tubes against the casing 16 as well as against each other. Thus, as shown in FIG. 5, a pair of clamping bands 36 may be employed at the upper and lower portions of the larger tubular fins 32, and additional clamping bands 33 and 35 may be employed around the upper and lower end portions of the inner tubular fins 31, as above described, the lower clamping bands 35 being engaged through the slots 34.

In the modification illustrated in FIG. 6, the inner tubular fins 31 are of circular cross-section, whereas the larger tubular fins, shown at 40, are of elliptical cross section with their major axes directed radially outwardly. The assembly of FIG. 6 is therefore substantially similar to that of FIGS. 4 and 5, except that a larger number of relatively large diameter outer tubular fins 40 may be employed than in the assembly of FIGS. 4 and 5 wherein the outer tubular fins 32 are of circular cross-sectional shape.

In the modification illustrated in FIG. 7, both the smaller tubular fins, shown at 45, and the larger tubular fins 40 are of elliptical cross-section and are positioned with their major axes directed radially outwardly, with the smaller elliptical tubular fins 45 received in the inner portions of the larger elliptical tubular fins 40.

In the embodiment illustrated in FIG. 8, the assembly is similar to that illustrated in FIG. 6 except that the larger fins, shown at 50, are generally elliptical in crosssection except that their inner end portions are conformably shaped so as to seat against the casing 16 with substantially continuous surfact contact. Thus, the inner edge portions of the otherwise elliptically shaped fins 50 are arcuately indented to conform with the arcuate surface contour of casing 16. As shown in FIG. 7

8, the relatively large tubular fins 50 completely surround the inner casing 16 and contain the cylindrical inner fins 31, said inner fins being clamped against the arcuately indented inner edge portions of fins 50 by their clamping bands 33 and 35.

As in the previously described embodiment of the invention, the outer fins 50 are clamped against the casing 16 by their metal clamping bands 36.

In the modification shown in FIG. 9, the inner tubular fins, shown at 60, are likewise of substantially elliptical cross-sectional shape and are located inside the larger elliptical fins 50 with their major axes substantially coincident, both the larger tubular fins 50 and the smaller tubular fins 60 being arcuately indented so as to conform with the arcuate contour of the liquid convection casing 16. The inner tubular fins 60 are clamped inwardly by their clamping bands 33 and 35 and the larger tubular fins 50 are clamped inwardly by their metal clamping bands 36, as in the previously described forms of the invention.

In the modification illustrated in FIG. 10, the arrangement is generally similar to that of FIGS. 4 and 5 except that the inner portions of the smaller and larger tubular fins are arcuately indented so as to conform with the arcuate contour of the liquid convection casing 16. Thus, the larger tubular fins, shown at 70, are arcuately indented at their inner portions to conform with the arcuate contour of casing 16, and the respective smaller tubular fins 71, received in tee tubular fins 70, are likewise arcuately indented to conform with the arcuately indented inner portions of the larger fins 70, the inner fins 71 being clamped inwardly by their metal clamping bands 33 and 35, and the larger tubular fins 70 being clamped inwardly by their metal clamping bands 36 in the same manner as above described. Clamping bands 36 clamp the fins 70 tightly against the liquid convection casing 16 and also tightly against each other.

Referring now to the form of the invention shown in FIGS. 11 to 14, a modified form of heat transfer assembly 80 is provided on the upper portion of the liquid convection casing 16. The transfer assembly 80 comprises a plurality of elongated fin members 81 of generally T-shape clamped together continuously and also clamped inwardly against the liquid convection casing 16 by a pair of metal clamping bands 82 and 83 surrounding their upper and lower end portions. Each fin 81 has an inner flange 84 having an arcuately concave inner end surface 85 conforming with the arcuate contour of the liquid convection casing 16. Each fin 81 is provided with an outer flange 86 having an arcuately convex outer contour 87 concentric with the arcuate contour of the inside surface 85 of the fin. Thus, as shown in FIG. 13, each fin may subtend an angle of 30 with reference to the center line of the associated liquid convection casing 16. The outer flange 86 may be provided with abutment ribs 87 providing for smooth abutment between adjacent fins with substantial heattransmitting contact area.

A continuous set of fins 81 is clamped around the upper portion of the casing 16 by the metal clamping bands 82 and 83, the contact ribs 87 of the fins being in abutting engagement with each other whereby the assembly defined is of substantially continuous outside radiation surface and a substantially continuous inside heat-conduction surface is in tight and flush contact with the liquid casing 16. The adjacent fins 81 thereby define between them respective convection channels 88 allowing atmospheric air to flow upwardly therethrough in the manner described in connection with FIGS. 1 and 2, to carry off heat conducted to the fins from the upper portion of casing 16.

The assembly may be mounted on the casing 16 at any desired position at its upper portions, preferably at a substantial height above ground level, as shown in FIG. 12.

As shown in FIGS. l5, 16, 17 and 18, the ductforming inside surfaces of the T-Shaped fins may be suitably corrugated or may be otherwise made of irregular contour so as to increase the heat-transmitting surface areas of the convection channels. Thus, as shown in FIGS. 15 and 16, one modified form of T-shaped member suitable for use in the manner disclosed in FIG. 11 is designated at 91 and is generally similar in shape to the previously described T-shaped member 81 except that its web 92 is formed with opposed outwardly tapering ribs 93,93 extending longitudinally for the full length of the T-shaped fin member and being located substantially at the intermediate portion of the web 92. The opposed outwardly tapering ribs 93,93 substantially increase the heat-transmitting surface area of the convention ductsdefined by the member 91 installed on the liquid casing 16 in the manner illustrated in FIGS. 11 and 12.

It will be further noted that the inner flanges of the T-shaped members may be formed with contact ribs 95,95 opposing the contact ribs 87', 87' of the outer flanges of the fins and having outer surfaces located in the same radial planes, relative to the center line of the associated liquid casing 16, as the outer surfaces of the abutment ribs 87'.

In the further modified form of T-shaped fin shown in FIGS. 17 and 18, the inside wall surfaces of the T- shaped fin shown at 96, are formed with continuously extending longitudinal spaced ribs 97 providing a corrugated surface contour for the ducts defined by the T- shaped fins when they are mounted on the casing 16 in the manner illustrated in FIGS. 11 and 12. In the typical corrugated surface arrangement illustrated in FIGS.

l7 and 18, the inside surfaces of the outer flanges of the fins and the adjacent wall surfaces of the webs 92' of the T-shaped fins are provided with the spaced longitudinal ribs 97, and the inwardly facing surfaces of the inner flanges 85 of the fins are formed with substantially semi-cylindrical inwardly facing cavities 98. Thus, the T-shaped fins, when mounted on a casing 16 in the amnner illustrated in FIGS. 11 and 12, define ducts which have relatively large heat-transmitting surface areas, facilitating the transmission of heat therefrom to the atmospheric air flowing upwardly by convection therethrough.

The convection casing 16 is preferably closed at its top end as well as at its bottom end, so that it defines a closed fluid system. The liquid convection system in casing 16 is in itself of well known construction and therefore it is deemed unnecessary to described the details thereof.

While certain specific embodiments of an improved thermal stabilizer assembly for use in stabilizing the temperature of masses of soil or other materials have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

l. A thermal stabilizer assembly comprising an elongated heat-conductive liquid convection casing adapted to be positioned upright in a body of matter with its upper portion projecting therefrom into the atmosphere, said casing containing fluid in which convection currents can be generated responsive to differences in temperature between the top and bottom portions of the casing, and a heat-transmitting assembly secured around the upper portion of said casing, said heat-transmitting assembly comprising a plurality of elongated heat-conductive fin elements disposed parallel and outwardly adjacent to the upper portion of the casing, means securing said fin elements to the casing, and means on the fin elements defining laterally closed air ducts leading from the bottom to the top ends of the fin elements, whereby convection atmospheric air currents may flow upwardly through said ducts and transfer heat from the upper portion of the casing to the atmosphere, wherein said fin elements are provided with lateral abutting portions held in abutting contact by said securing means, and wherein said fin elements are substantially T-shaped in cross-section and wherein said lateral abutting portions comprise the edges of the inner and outer flanges of the T-shaped fin elements.

2. The thermal stabilizer assembly of claim 1, and wherein said securing means comprises at least one heat-conductive clamping band surrounding and clampingly engaging said fin elements.

3. The thermal stabilizer assembly of claim 1, and wherein saidsecuring means comprises a plurality of heat-conductive clamping bands surrounding and clampingly engaging spaced portions of said fin elements.

4. The thermal stabilizer assembly of claim 1, and wherein the T-shaped fin elements have flanges at their inner edges arcuately curved to substantially conform with the contour of the casing.

5. The thermal stabilizer assembly of claim 1, and wherein the abutting side edges of the flanges of the T- shaped fin elements lie substantially in radial planes relative to the axis of the casing.

6. The thermal stabilizer assembly of claim 1, and wherein the duct-forming surface of at least one of the T-shaped fin elements is ribbed to increase its heattransmitting surfacearea.

7. The thermal stabilizer assembly of claim 1, and wherein the outer flanges of the T-shaped fin elements are formed with abutment ribs having substantially smooth abutment surfaces.

8. The thermal stabilizer assembly of claim I, and wherein the web portions of the T-shaped fin elements are provided on their opposite surfaces with ribs to increase their heat-transmitting surface areas.

9. The thermal stabilizer assembly of claim 1, and wherein the duct-forming surfaces of the T-shaped fin elements have a plurality of spaced longitudinal ribs to increase their heat-transmitting surface areas.

The thermal stabilizer assembly of claim 1, and wherein the web portions of the T-shaped fin elements are formed with opposed outwardly tapering rigs to increase their heat-transmitting surface areas.

* III F III 

1. A thermal stabilizer assembly comprising an elongated heatconductive liquid convection casing adapted to be positioned upright in a body of matter with its upper portion projecting therefrom into the atmosphere, said casing containing fluid in which convection currents can be generated responsive to differences in temperature between the top and bottom portions of the casing, and a heat-transmitting assembly secured around the upper portion of said casing, said heat-transmitting assembly comprising a plurality of elongated heat-conductive fin elements disposed parallel and outwardly adjacent to the upper portion of the casing, means securing said fin elements to the casing, and meaNs on the fin elements defining laterally closed air ducts leading from the bottom to the top ends of the fin elements, whereby convection atmospheric air currents may flow upwardly through said ducts and transfer heat from the upper portion of the casing to the atmosphere, wherein said fin elements are provided with lateral abutting portions held in abutting contact by said securing means, and wherein said fin elements are substantially T-shaped in cross-section and wherein said lateral abutting portions comprise the edges of the inner and outer flanges of the T-shaped fin elements.
 2. The thermal stabilizer assembly of claim 1, and wherein said securing means comprises at least one heat-conductive clamping band surrounding and clampingly engaging said fin elements.
 3. The thermal stabilizer assembly of claim 1, and wherein said securing means comprises a plurality of heat-conductive clamping bands surrounding and clampingly engaging spaced portions of said fin elements.
 4. The thermal stabilizer assembly of claim 1, and wherein the T-shaped fin elements have flanges at their inner edges arcuately curved to substantially conform with the contour of the casing.
 5. The thermal stabilizer assembly of claim 1, and wherein the abutting side edges of the flanges of the T-shaped fin elements lie substantially in radial planes relative to the axis of the casing.
 6. The thermal stabilizer assembly of claim 1, and wherein the duct-forming surface of at least one of the T-shaped fin elements is ribbed to increase its heat-transmitting surface area.
 7. The thermal stabilizer assembly of claim 1, and wherein the outer flanges of the T-shaped fin elements are formed with abutment ribs having substantially smooth abutment surfaces.
 8. The thermal stabilizer assembly of claim 1, and wherein the web portions of the T-shaped fin elements are provided on their opposite surfaces with ribs to increase their heat-transmitting surface areas.
 9. The thermal stabilizer assembly of claim 1, and wherein the duct-forming surfaces of the T-shaped fin elements have a plurality of spaced longitudinal ribs to increase their heat-transmitting surface areas.
 10. The thermal stabilizer assembly of claim 1, and wherein the web portions of the T-shaped fin elements are formed with opposed outwardly tapering ribs to increase their heat-transmitting surface areas. 